The pharmaceutical industry uses a wide variety of tests to evaluate active pharmaceutical ingredients and pharmaceutical compositions. These tests are used to characterize the performance of the candidates and/or compositions over a wide range of conditions. Ideally, such tests predict the in vivo performance of the candidate or composition, thus minimizing the number of in vivo tests needed to evaluate and select candidates, reducing development time and costs.
Much of the prior art is focused on estimating the intrinsic in vivo permeability of drugs through the epithelial membrane in the GI tract from in vitro test data. Several of these in vitro tests utilize a membrane to aid in predicting in vivo performance. The state of the art is summarized in many articles, including, for example, “Assessing the Absorption of New Pharmaceuticals,” by Hidalgo in Current Topics in Medicinal Chemistry, 2001, 1, 385-401, and “High Throughput Physicochemical Profiling for Drug Discovery,” J. Pharm Sci., 2001, 90(11), 1838-1858.
Several of these in vitro membrane-based tests utilize cultured cell lines, including Caco-2, HT-29, and MDCK cells. Examples of devices for performing such tests are described in U.S. Pat. Nos. 5,962,250, 6,022,733, and 6,043,027. However, such methods are time consuming, expensive, and often give widely varying results. In addition, such tests are generally designed for estimating the intrinsic permeability of individual compounds through the epithelial membrane. While effective for this, they are not always effective for evaluating the rate of absorption for pharmaceutical compositions.
Other tests utilize artificial or synthetic membranes to estimate the in vivo absorption and intrinsic permeability of individual compounds. These tests include immobilized artificial membrane (IAM) columns, the parallel artificial membrane permeation assay (PAMPA), and filter-immobilized artificial membranes. Methods and equipment for performing such tests are disclosed in numerous literature references, including Kansy et al., J. Med. Chem., 1998, 41, 1007-1010; Wohnsland and Faller, J. Med. Chem., 2001, 44, 923-930; Sugano et al., Intl. J. Pharmaceutics, 228 (2001) 181-188; Sugano et al., J. Biomolecular Screening, 6(3) (2001) 189-196; Sugano et al., Intl. J. Pharmaceutics, 241 (2002) 241-251; Zhu et al., Eur. J. Med. Chem., 37 (2002) 399-407; Avdeef et al., Eur. J. Pharm. Sci., 14 (2001) 271-280.
While the prior-art methods and devices may be suitable for estimating the intrinsic permeability of individual compounds in vivo, the inventors have discovered that they have significant limitations. Generally, the methods are not suitable for evaluating low-solubility drugs. In addition, the methods often do not adequately predict the rate of absorption of drugs from pharmaceutical compositions. In the prior-art test methods and devices, the permeate side of the membrane contains a solution (sometimes referred to as the acceptor solution in the art) similar to that used on the feed side (sometimes referred to as the donor solution in the art), while the membrane contains an organic or lipid solution, sometimes in the form of a bilayer membrane. In such cases, the permeate solution does not act as a sink for the drug, severely limiting the driving force for transport across the membrane, especially for low solubility drugs. While additives have been added to the permeate solution to improve the solubility of the drug therein, such additives do not work for all drugs and can destabilize the membrane. In addition, the prior art methods do not correlate well with in vivo results, especially for drugs that partition into bile salt or lecithin micelles present in vivo, nor do they correlate well with solubilized drug forms.
Thus, there is a continuing need in the art to develop effective and efficient methods for estimating the in vivo absorption rate for drugs present in pharmaceutical compositions.